Question: On the first 6 exams of his geometry class, Ben got an average score of 79. What does he need on the next exam to have an overall average of 81?
Answer: Let his score on the next exam be $x$ The sum of all of his scores is then $6 \cdot 79 + x$ The same sum must also be equal to $7 \cdot 81$ Solve: $x = 7 \cdot 81 - 6 \cdot 79 = 93$.